Update to wagtail-factories==2.1.0

Changelog: https://github.com/wagtail/wagtail-factories/compare/2.0.1...2.1.0

2.1.0
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 - Add support for Wagtail 3.0 and drop support for all Wagtail versions
   before 2.15
 - Add support for Django 4.0
 - Add support for Python 3.10
 - Removed support for Python 3.6
 - Removed support for Django 2.2 and 3.1
 - Removed support for factory boy <3.2